This invention concerns a two-step oxidation process for making polyisobutylcarboxylic acids by ozonizing polyisobutylene and then contacting the ozonized polyisobutylene with nitric acid.
High molecular weight carboxylic acids, and derivatives thereof, having long hydrocarbon chains terminated at one end by a carboxyl group are useful in hydrocarbon fuels and oils for a variety of purposes. Polyisobutylenes which are derived from isobutylene and which contain a potentially oxidizable olefinic link at or near the terminal carbon atom are potential sources of such long chain carboxylic acids. Procedures described in the art for oxidizing polyisobutylenes are usually unsatisfactory for producing polyisobutylcarboxylic acids in practical amounts uncontaminated by troublesomely large proportions of neutral polyisobutylene derivatives.
For instance, the ozonization of polyisobutylenes disclosed in U.S. Pat. Nos. 2,461,966 and 3,715,313 produces neutral oxygenated products, (aldehydes and ketones) and very little carboxylic acid. U.S. Pat. No. 3,715,313 discloses oxidation of ozonized polyisobutylenes with hydrogen peroxide to form a carboxylic acid component which can be removed from the reaction mixture by extraction with aqueous sodium carbonate solution and then with water. Such carboxylic acid component evidently constitutes a minor proportion of the oxidized mass, the major (unextracted) portion being disclosed as a neutral carbonyl-containing component, e.g. a ketone.
U.S. Pat. No. 3,931,024 teaches making high molecular weight oxygenated polyolefin reactants by heating the polymer in the presence of air. British patent specification No. 1,172,818 teaches the making of ketones by ozonizing a polyolefin and treating the ozonized polyolefin with hydrogen. British patent specification No. 1,027,410 discloses the oxidation of polyisobutylenes with nitric acid. Such a procedure, however, produces an acidic mixture containing only a small proportion of carboxylic acids, the large proportion being made up of aliphatic nitro compounds.
Nonoxidative procedures for converting polyisobutylenes to long chain carboxylic acids are known. For instance, condensation of polyisobutylenes with maleic anhydride provides polyisobutenylsuccinic anhydrides. U.S. Pat No. 3,219,666 discloses preparation of polyisobutenylcarboxylic acids by chlorinating a polyisobutylene, converting the chlorinated product to the corresponding nitrile, and hydrolyzing the nitrile to the carboxylic acid. U.S. Pat. No. 3,897,224 discloses condensation of acids or esters with long chain olefin polymers in the presence of halogen. Generally, all such nonoxidative procedures produce acids which are characterized by poor oxidative stabilities and poor hydrolytic stabilities of their derivatives.
Needed, then, is a practical and efficient process for substantially completely converting polyisobutylenes to polyisobutylcarboxylic acids which acids are characterized by good oxidative stabilities and good stabilities of their derivatives.